Microservices

Figure 1. NATS Architecture Component Diagram NATS is a high-performance messaging system that offers simplicity, speed, and scalability. It is particularly suited for building distributed systems and microservices. This article demonstrates how to integrate NATS with Java, showcasing the essential steps to set up, connect, and publish/subscribe to messages. Prerequisites Before diving in, we should ensure to have the following installed: Java Development Kit (JDK) 11 or later. Maven or Gradle for dependency management. Docker (optional). ...

The following WebFilter redirects incoming requests for / to a static HTML file, index.html. ToIndexPageRedirection.java package com.hascode.tutorial; import org.springframework.stereotype.Component; import org.springframework.web.server.ServerWebExchange; import org.springframework.web.server.WebFilter; import org.springframework.web.server.WebFilterChain; import reactor.core.publisher.Mono; @Component public class ToIndexPageRedirection implements WebFilter { @Override public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) { if (exchange.getRequest().getURI().getPath().equals("/")) { return chain.filter( exchange.mutate().request( exchange.getRequest().mutate().path("/index.html").build() ).build() ); } return chain.filter(exchange); } } Ressources: JavaDocs WebFilter

Goals Package a Spring Boot Service as RPM Package Configure systemd integration Add install/uninstall hooks to create users, directories etc. Maven Setup <?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.4.2</version> <relativePath/> </parent> <groupId>com.hascode</groupId> <artifactId>sample-app</artifactId> <version>1.0.0-SNAPSHOT</version> <name>sample-app</name> <properties> <java.version>11</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-actuator</artifactId> </dependency> </dependencies> <build> <plugins> <plugin> (1) <groupId>de.dentrassi.maven</groupId> <artifactId>rpm</artifactId> <version>1.5.0</version> <executions> <execution> <goals> <goal>rpm</goal> </goals> </execution> </executions> <configuration> <packageName>sample-app</packageName> <skipSigning>true</skipSigning> <group>Application/Misc</group> <requires> <require>java-11-openjdk-headless</require> (2) </requires> <entries> <entry> (3) <name>/opt/sample-app</name> <directory>true</directory> <user>root</user> <group>root</group> <mode>0755</mode> </entry> <entry> (4) <name>/opt/sample-app/log</name> <directory>true</directory> <user>sample-app</user> <group>sample-app</group> <mode>0750</mode> </entry> <entry> (5) <name>/opt/sample-app/sample-app.jar</name> <file>${project.build.directory}/${project.build.finalName}.jar</file> <user>root</user> <group>root</group> <mode>0644</mode> </entry> <entry> (6) <name>/usr/lib/systemd/system/sample-app.service</name> <file>${project.basedir}/src/main/dist/sample-app.service</file> <mode>0644</mode> </entry> </entries> <beforeInstallation> (7) <file>${project.basedir}/src/main/dist/preinstall.sh</file> </beforeInstallation> <afterInstallation> <file>${project.basedir}/src/main/dist/postinstall.sh</file> </afterInstallation> <beforeRemoval> <file>${project.basedir}/src/main/dist/preuninstall.sh</file> </beforeRemoval> <license>All rights reserved</license> </configuration> </plugin> </plugins> </build> </project> ...

The OpenAPI and Swagger API description format are becoming important standards to specify API contracts for RESTful web services and the Microservices trend pushes the need for such contracts even further. Therefore arises the need for software architects, testers and developers to write tests to verify if an exposed API follows such a specified contract. In the following tutorial I will demonstrate a setup with Java, Maven, JUnit and the designated contract-testing-library, assertj-swagger that verifies the validity of such a contract exposed by a Spring Boot application against a local stored definition. ...

When dealing with remote services or APIs there is always the risk of latency issues, failures or connection losses. The worst thing to happen is when the remote service is down and our application hangs until the underlying protocol’s (e.g. TCP) connection timeout is reached and we’re receiving an exception. Until this moment is reached, our application might hang, memory is allocated for threads or bound objects and at last, our continuous requests might prevent the remote system from recovering. ...

When it comes to writing microservices in Java, plenty of tools and frameworks exist. In the following tutorial, I’d like to demonstrate another minimalistic framework called Bootique by implementing a simple microservice exposing its functions either as a RESTful web-service or as a runnable command executed using the command line. Bootique Command Line Dependencies Using Maven here, we’re adding the following elements to our project’s pom.xml: Bootiques Bill of Materials as dependency management: bootique-bom Bootique Jersey for our REST service: bootique-jersey Bootique Logback for logging: bootique-logback Maven Shade Plugin to assemble our fat-jar ...

Spring Boot allows us to create RESTful web-services with ease, Swagger specifies a format to describe the capabilities and operations of these services and with Swagger UI it is possible to explore our REST API with a nice graphical user interface in our browser. Springfox is a project that aims at creating automated JSON API documentation for API’s built with Spring and is used in the following tutorial to integrate Swagger into a sample application. ...

A variety of different tools exists to help us analyze RESTful web-services and create documentations for their APIs in different formats. In the following tutorial I’d like to demonstrate how to document an existing JAX-RS web-service in multiple formats like Swagger, AsciiDoc or Plain Text using Maven, the JAX-RS Analyzer and the JAX-RS Analyzer Maven Plugin. The JAX-RS Analyzer gathers its information not only by reflection like most other tools but also by bytecode analysis and therefore does not require us to add special annotations for documentation to our code. ...

Having written about the basics of using Cucumber in a Java project in my last blog article, I now would like to demonstrate how to use a similar setup in a Java EE web project with Arquillian and the Cukespace library. In the following tutorial, we’re going to write a full Java EE web application and add BDD-style tests to the project so that we’re able to test our business layer on the one hand and the user interface on the other hand using Arquillian Drone and Selenium. ...

Because a lot of my current projects are using JAX-RS in different versions I’d like to write down and share some frequently used snippets for implementing RESTful web-services with the JAX-RS specification here. Using RegEx in Path Expressions Sometimes we need to extract multiple parameters from a path expression e.g. in the following example where year, month and day are fragments if the path. @GET @Path("/orders/{year:\\d{4}}-{month:\\d{2}}-{day:\\d{2}}") @Produces(MediaType.TEXT_PLAIN) public Response getOrders(@PathParam("year") final int year, @PathParam("month") final int month, @PathParam("day") final int day) { return Response.ok("Year: " + year + ", month: " + month + ", day: " + day).build(); } ...